Rectifier circuit with a voltage sensor

ABSTRACT

A rectifier circuit with a synchronously controlled semiconductor element comprising at least one field effect transistor with a control electrode and two switching electrodes. The control electrode operates the reverse state and the forward state between the switching electrodes. For this, the rectifier circuit comprises at least one driver which cooperates with a voltage sensor of the field effect transistor. During the diode operating state of the field effect transistor, the driver operates this to the forward state. The voltage sensor thereby forms at least one part of a non-linear voltage divider which comprises at least one monolithically integrated measuring capacitance.

BACKGROUND

The application relates to a rectifier circuit with at least one fieldeffect transistor which includes a control electrode and two switchingelectrodes. The control electrode thereby operates the field effecttransistor from a reverse state to an opening state and vice versabetween the two switching electrodes and vice versa. The rectifiercircuit furthermore includes one driver which cooperates with a voltagesensor of the field effect transistor and which operates this to theforward state with the diode operating state of the field effecttransistor.

During the switching from the reverse state into the forward state, aresidual voltage remains in the diode operation, which voltage can leadto large forward losses with synchronous rectifier circuits. It istherefore necessary to provide at least one field effect transistorwhich switches to the forward state in a timely manner. However, thisrequires a measuring technique which signals a driver of the fieldeffect transistor in a timely manner that it shall connect and pass fromthe diode forward operation to the channel conducting state. However, inthis transition phase, voltage peaks paired with very high voltage andcurrent changes per time unit dv/dt and di/dt can occur, which are amultiple of the voltage to be realized in the diode forward operation.

During a measurement of the voltage in the diode opening operationbetween source and drain by using an integrated circuit, the integratedmeasuring circuit thus has to have a high electrical strength at theinlet, so that it can recognize the diode opening operation safelydespite high voltage peaks and is protected against overvoltage peaks.

Another solution consists in cutting the high voltage part at the drainof a field effect transistor via a diode, so that the input for theintegrated measuring circuit is drawn to a reference potential. But assoon as the voltage drops below 5 V, the diode becomes conducting, sothat it is possible to use an integrated measuring circuit with an inputwith a low electrical strength, so as to detect the voltage in the diodeopening operation at such a field effect transistor in a timely manner.

However, the last-mentioned possibility requires additional componentsas for example diodes, so as to ensure that the integrated circuit isprotected from occurring voltage peaks. The known possibilities are thuscost-intensive solutions which require a complex circuit on the one handand result in a restriction of the lift of the wanted signal for thevoltage sensor.

For these and other reasons, there is a need for the present invention.

SUMMARY

An embodiment includes a rectifier circuit with a synchronouslycontrolled semiconductor component. The rectifier circuit includes atleast one field effect transistor with a control electrode and twoswitching electrodes. The control electrode controls the reverse stateand the forward state between the switching electrode. For this, therectifier circuit includes at least one driver which cooperates with avoltage sensor of the field effect transistor. In the diode operatingstate of the field effect transistor, the driver operates the fieldeffect transistor into the forward state. The voltage sensor therebyforms at least one part of a non-linear voltage divider.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying drawings are included to provide a furtherunderstanding of the present invention and are incorporated in andconstitute a part of this specification. The drawings illustrate theembodiments of the present invention and together with the descriptionserve to explain the principles of the invention. Other embodiments ofthe present invention and many of the intended advantages of the presentinvention will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

FIG. 1 illustrates an equivalent circuit diagram of a non-linearcapacitive voltage divider with connection of a voltage sensor of asynchronous rectifier circuit in principle;

FIG. 2 illustrates a schematic plan view of a semiconductor componentfor a synchronous rectifier circuit according to FIG. 1;

FIG. 3 illustrates a schematic cross section of a partial region of afield effect transistor for a synchronous rectifier circuit according toFIG. 1;

FIG. 4 illustrates an equivalent circuit diagram of a non-linearcapacitive voltage divider with connection of a voltage sensor of asynchronous rectifier circuit in principle;

FIG. 5 illustrates a schematic plan view of a semiconductor component Ofa synchronous rectifier circuit according to FIG. 4;

FIG. 6 illustrates a schematic cross section of a partial region of afield effect transistor for a synchronous rectifier circuit according toFIG. 4;

FIG. 7 illustrates an equivalent circuit diagram of a furtherpossibility for voltage limitation in principle;

FIG. 8 illustrates a schematic cross section of a possible realizationof the equivalent circuit diagram in principle according to FIG. 7;

FIG. 9 illustrates a schematic plan view of a possible realization ofthe equivalent circuit diagram in principle according to FIG. 7;

FIG. 10 illustrates an equivalent circuit diagram of a non-linearcapacitive voltage divider for a synchronous rectifier circuit inprinciple;

FIG. 11 illustrates a schematic cross section of a partial region of afield effect transistor with field plate structures for a synchronousrectifier circuit according to FIG. 10;

FIG. 12 illustrates a schematic plan view of a semiconductor componentwith a field effect transistor according to FIG. 11 in a housing, andwith outer connections;

FIG. 13 illustrates a simplified equivalent circuit diagram of asemiconductor component for a synchronous rectifier circuit inprinciple;

FIG. 14 illustrates a schematic plan view of a monolithically integratedovervoltage protection diode of polysilicon;

FIG. 15 illustrates a schematic plan view of a monolithically integratedexcess voltage protection diode of polysilicon.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following Detailed Description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” etc., is used withreference to the orientation of the Figure(s) being described. Becausecomponents of embodiments of the present invention can be positioned ina number of different orientations, the directional terminology is usedfor purposes of illustration and is in no way limiting. It is to beunderstood that other embodiments may be utilized and structural orlogical changes may be made without departing from the scope of thepresent invention. The following detailed description, therefore, is notto be taken in a limiting sense, and the scope of the present inventionis defined by the appended claims.

FIG. 1 illustrates an equivalent circuit diagram of a non-linearcapacitive voltage divider 7 with connection of a voltage sensor 2 for asynchronous rectifier circuit. For this, the output capacitance Ca of asensor region 38 is used as a non-linear high voltage capacitance, inwhich this output capacitance Ca is voltage-dependent and represents aparallel circuit of the voltage-dependent feedback capacitance Cgd andthe voltage-dependent drain source capacitance Cds of the sensor region38. The sensor region 38 includes a sensor source s, a sensor drain dand a sensor gate g and is monolithically integrated in a maintransistor 39 which is a field effect transistor 3 of the synchronousrectifier circuit. If it is not bypassed by outside switching methods,the sensor region additionally includes a virtually voltage-independentgate source capacitance Cgs.

The main transistor 39 has a first 5 and a second switching electrode 6in the form of a source S and a drain D of the field effect transistor3. The main transistor 39 further includes a control electrode 4 in theform of the gate G of the field effect transistor 3 which controls thereverse state and the forward state of the field effect transistor 3.

For a low voltage tap 41, a voltage-independent measuring capacitance Cmis used, which is formed by an externally connected capacitance Cext,and which is connected between the mass and a measuring point MP of thenon-linear capacitive voltage divider 7 in this embodiment. Thevoltage-dependent output capacitance Ca of a field effect transistortypically varies between 0 V and the maximum breakthrough voltage of thefield effect transistor by approximately one magnitude. That is, if ameasuring capacitance Cm with the magnitude of half the outputcapacitance Ca/2 applied of a sensor region 38 at 0 V is applied, ⅔ ofthe voltage drop is obtained during the diode operation of the fieldeffect transistor, that is, approximately 0.5 V as voltage drop at themeasuring capacitance Cm.

FIG. 2 illustrates a schematic plan view of a semiconductor component 1for a synchronous rectifier circuit according to FIG. 1. A common drainof d and D, as illustrated in FIG. 1 for the sensor region 38 or themain transistor 39, is arranged on the bottom side of a semiconductorchip as back side metallization, not visible here. The largest part ofthe upper side of the semiconductor which is visible here is taken up bythe source metallization 12 of the cell field 11 of the field effecttransistor 3 or the electrode of the source S of the main transistor 39.A smaller surface is reserved for the control electrode, the gate G ofthe field effect transistor 3. A part of the cell field 11 of the maintransistor is provided for the monolithically integrated sensor region38. This sensor cell field 10 is not different from the cell field 11 ofthe main transistor 39 in its semiconductor structure and is onlyseparated electrically from the cell field by an insulation region 42surrounding the sensor cell field 10.

FIG. 3 illustrates a schematic cross section of a partial region of asemiconductor component 1 for a synchronous rectifier circuit accordingto FIG. 1. This partial region illustrates the sensor cell region 10 andthe cell region 11 with active cells of the field effect transistor 3.Between the sensor cell region 10 and the cell region 11 is arranged afield plate trench 32 with a field plate 8 surrounding the sensor cellregion 10, so as to insulate and shield the sensor cell region 10 fromthe cell field 11.

The sensor cell region 10 and the cell field 11 can in principle bemanufactured simultaneously and with identical method processes. Onlythe source metallization is separated with the field plate 8 into asource metallization 12 of the cell field and a source metallization 13of the sensor cell region 10 by the surrounding field plate trench 32.Thus, some of the cells of the field effect transistor 3 are executed asa separate sensor cell region 10 and have a separate sourcemetallization 13.

In the region of the sensor cell region 13, the gate or the controlelectrode 4 of the trench gate structure 14 is bypassed with the sourcemetallization 13, as illustrated by the connection lines 37. Thisprevents a floating of the gate or the control electrode 4 or anunintentional opening of the channel at a positive voltage at the gaterelative to the source in the sensor cell region 10. The structure canbe realized with classical trench gate cells or, as later illustrated inFIG. 11, also with field plate trenches and with a separate fieldelectrode.

In this embodiment, p-wells for the body zones 24 of the sensor cellregion 13 are electrically separated from the active cells of the fieldeffect transistor 3. This electric separation is ensured by theabove-mentioned surrounding field plate trench 32 or by a correspondinglip. The voltage sensor connection VS which is guided outwardly canthereby be connected to the source metallization 13 of the sensor cellregion 10 as a measuring point MP. An access via the outer contact 30illustrated in FIG. 1 is possible on this voltage sensor connection VS.In this embodiment according to FIG. 3, the dielectric of themonolithically integrated capacitance is formed partially by a gateoxide 15 of the trench gate structure 14 in the sensor cell region 10.

The low voltage which is present between the source S and the drain Dduring the conducting diode operating state of a body diode of the fieldeffect transistor 3 is detected securely with the non-linear voltagedivider 7. This is particularly useful with low voltage MOSFETs with areverse capability between 20 and 200 Volts, especially as voltage peaksup to 100 V paired with very high dv/dt and di/dt values can occur intypical applications for example with an output of 12 V of a synchronousrectifier. These voltage peaks will not be effective at the measuringpoint MP by the non-linear voltage divider 7, so that measuring, controland/or driver ICs can be employed for the synchronous rectifier in acost-effective manner with a correspondingly reduced reverse capability.

FIG. 4 illustrates an equivalent circuit diagram of a non-linearcapacitive voltage divider 7 with connection to a voltage sensor of asynchronous rectifier circuit in principle. Components with the samefunctions as in the previous figures are characterized with the samereference numerals and are not mentioned especially. In this embodiment,a field effect transistor 3 also includes a sensor cell field as sensorregion 38 with a separate sensor gate g insulated from the maintransistor 39. The sensor output capacitance of the monolithicallyinsulated sensor region 38 forms a voltage-dependent measuringcapacitance of the non-linear voltage divider 7. However, the sensorgate g is electrically connected to the source S of the main transistor39, so that the gate source capacitance Cgs of the sensor region 38forms a virtually voltage-independent reference capacitance of thenon-linear voltage divider 7.

This gate source capacitance Cgs is usually large enough with regard tothe output capacitance of the sensor region 38, so as to form aneffective non-linear voltage divider 7. For a low voltage tap 41, avoltage-independent external measuring capacitance can thus be forgone,which is formed by an externally connected capacitance Cext and which isconnected between the mass and a measuring point MP of the non-linearcapacitive voltage divider 7 in this embodiment. An additional externalvoltage-independent capacitance can optionally be connected in parallel,as characterized by the by the dashed lines in FIG. 4.

FIG. 5 illustrates a schematic plan view of a semiconductor component 1for a synchronous rectifier circuit according to FIG. 4. In contrast toFIG. 2, the sensor gate g is electrically connected to the source S viaa connection line 43.

FIG. 6 illustrates a schematic cross section of a partial region of afield effect transistor 3 for a synchronous rectifier circuit accordingto FIG. 4. In this embodiment, the sensor cell region 10 and the cellfield 11 of the field effect transistor 3 are formed with a lateral gatestructure. In the sensor cell region 10, the lateral control electrodes4 form a virtually voltage-independent capacitance with the sourcemetallization 13 of the sensor cell region 10, which represents areference capacitance for an entirely monolithically integrated voltagedivider, so that an external capacitance is unnecessary.

FIG. 7 illustrates an equivalent circuit diagram of a furtherpossibility for the voltage limitation of the signal at the measuringpoint MP in principle. For this, the p-wells of the sensor region on themeasuring potential have to be connected with an n-channel MOStransistor 21 in a self-regulating manner with the p-wells on the sourcepotential of the main transistor 39. For this, the n-channel MOSFET 21is arranged between the measuring point MP and the source connection S,and the gate of the n-channel MOSFET 21 is connected to the measuringpoint MP.

FIG. 8 illustrates a schematic cross section for this and FIG. 9illustrates a plan view of a possible realization in silicon. In thecase of the trench gate technology illustrated in FIGS. 8 and 9, twospatially separated p-wells are connected to corresponding n+ sourceimplantations via a trench, the gate metallization of which lies on themeasuring point MP potential. Sidewall transistors are arranged betweenthe sensor cell region 10 of the voltage sensor 2 and the cell field 11of the main transistor 39 as voltage-limiting n-channel MOSFET 21, asillustrated by the plan view in FIG. 9.

It is further possible that the source metallization 13 of the sensorcell region 10 bypasses trench gate structures 14 and the field platestructures, so as to create a larger voltage-dependent monolithicallyintegrated capacitance. The field plate trenches can also be executedwith a field plate lying on the gate potential or as a planartechnology. It is finally also possible that field plate structures arearranged in a floating manner in the sensor cell region and that trenchgate structures are bypassed with the source metallization 13 of thesensor cell region.

FIG. 10 illustrates an equivalent circuit diagram of a non-linearcapacitive voltage divider for a synchronous rectifier circuit of afurther embodiment in principle. In this embodiment, no separatemonolithically integrated sensor region is provided, but thecapacitances of field plates of a field effect transistor 3 are used forthe voltage sensor. The capacitances of the field plates of the fieldeffect transistor 3 opposite the source CFpS, drain CFpD and gate CFpGare used as voltage-dependent non-linear high voltage capacitance of thenon-linear capacitive voltage divider. A voltage-independent measuringcapacitance CM is provided for a low voltage tap which is formed by anexternally connected capacitance Cext and which is connected between themass and a measuring point MP of the non-linear capacitive voltagedivider in this embodiment.

With such a circuit in principle, negative drain source Voltages in lowor medium voltage field effect transistors 3 in the region of forexample between 6 V to 200 V can be realized with high precision.However, positive drain source voltages do not have to be measured.

FIG. 11 illustrates a schematic cross section of a partial region of afield effect transistor 3 with field plate structures 16 for asynchronous rectifier circuit according to FIG. 10. Such a field platestructure 16 can be used to use the capacitances of the field plates ofthe field effect transistor 3 opposite the source CFpS, drain CFpD andgate CFpG as voltage-dependent non-linear high voltage capacitance ofthe non-linear capacitive voltage divider. The field plate oxide 9and/or the gate oxide of a trench gate structure 14 illustrated hereform the dielectric of the capacitances opposite the drain CFpD and/orgate CFpG or source CFpS, in which the measuring point MP for anon-linear voltage divider can be lead out of a housing as an externalFP/VS connection, so as to be able to connect a voltage-independentreference capacitance for the non-linear voltage divider.

The field effect transistor 3 includes a trench gate structure 14 inthis cross sectional view next to the field plates 8 in the field platestructure 16, which is arranged in the same trench structure 20 as thefield plates 8. The trench gate structures 14 of the cell field 11 ofthe field effect transistor 3 are connected together as a controlelectrode 4 as the gate G of the field effect transistor 3. A sourcemetallization 13 of the first switching electrode 5, which is formed asa source S, contacts p-conducting body zones 24 and highly-dopedn+-conducting source zones 25. When a corresponding control voltage ispresent at the control electrode 4, channels 26 are formed in the bodyzones 24 between the source zones 25 and the n-conducting drift zones27, which enables a connection from the first switching electrode 5 tothe second switching electrode 6, which here represents a drainelectrode 6 of the drain D.

The measuring point MP cooperates with a measuring, control and/ordriver IC 44, as illustrated in the equivalent circuit diagram 10 inprinciple. The measuring point MP of the non-linear voltage divider canbe lead out from a standard housing of a power MOSFET as the connectionFP/VS, as illustrated in FIG. 12.

The field plate electrode 8 has a significant overlap with the drain Dvia its field oxide structure and can thus be used as voltage sensor.The field plate electrode 8 furthermore possesses a highly non-linearcharacteristic by its position deep in the space charging zone region ofthe drift passage, so that, when high reverse voltages of the potentialare present at the field plate sensor, a low positive voltage can beachieved during switching with an external capacitances Cext via themeasuring point MP. This is important, as, when positive voltages arepresent which are too high, the breakdown voltage of the field effecttransistor is influenced in a negative manner. The closing resistor ofthe transistor is not influenced in a negative manner by the field platevoltage sensor, the gate electrode and the channel region remainunaffected. Thus, no separate chip surfaces for a voltage sensor regionare necessary for this embodiment.

When the field plate electrode 8 is used only partially as voltagesensor, the breakthrough voltage of the region used as the voltagesensor is sometimes increased compared to the main transistor surface.This can for example take place by reducing the measuring width betweenthe trench structures. But this only has to be used when the voltagesensor surface is noticeably smaller than the main transistor.Otherwise, the breakthrough voltage of the main transistor has to beincreased compared to the one of the voltage sensor.

FIG. 12 illustrates a schematic plan view of a semiconductor componentwith a field effect transistor according to FIG. 11 in a housing, andwith outer connections 28 29, 30 and 31. The outer connection 28 isthereby in contact with the source electrode S of the field effecttransistor within the housing 22, the outer connection 29 contacts thecontrol electrode or the gate G of the field effect transistor in thehousing 22 and the outer connection 31 contacts the drain electrode D ofthe field effect transistor. The field plate connection FP/VS of themeasuring point MP is arranged between the gate G and the drain Dconnection. This outer contact FP/VS is in electrical connection withthe field plates within the field effect transistor. Avoltage-independent reference capacitance can be connected to thisconnection, so as to realize a non-linear voltage divider. One advantageof this embodiment is that, no additional semiconductor chip surface isrequired for the construction of a non-linear voltage divider inprinciple. Rather, the field plates typically on source potential whichare present in the field plate transistor 3 and which can be contacted,are partially or entirely used as voltage sensor on the entiresemiconductor chip surface.

Alternatively, the voltage at the monolithically integrated sensor canbe limited effectively by a n-channel MOSFET forward a source and sensoras illustrated in the above FIG. 7, or by a diode, as illustrated in thefollowing FIG. 13.

FIG. 13 illustrates a simplified equivalent circuit diagram of asemiconductor component in principle, which is provided for asynchronous rectifier circuit and includes a voltage sensor connectionVS having an overload protection. Although a non-linear voltage divideris already realized by the voltage-dependent field plate capacitanceCFpD and the external voltage-independent reference capacity, theabove-mentioned danger of a reduction of the breakthrough stability ofthe field effect transistor 3 is removed by the diode 17 which isclamped between the source and the field plate electrode. In addition,this diode 17 should ensure that the potential at the measuring point MPremains negative and that the voltage present at the measuring point MPis clamped to 2 to 3 volts.

Such a diode 17 can be arranged between the field plate electrode andthe metallic contact of the source S of the main transistor, asillustrated in FIG. 14.

FIG. 14 illustrates a schematic plan view of a monolithically integratedovervoltage protection diode 19 of polysilicon. For this, the outerconnection VS for the voltage sensor is guided via a metallic conductor33 to a p-conducting poly region which is applied to the semiconductorbody which abuts an n-conducting polysilicon region. The n-polyregionalso includes a metallic conductor 34 which is in electrical connectionwith the source S.

The diode 17 illustrated in FIG. 13 can be realized as a Schottky diodebetween the field plate electrode and the metallic contact to the sourceS of the main transistor, as illustrated in FIG. 15.

FIG. 16 illustrates a schematic plan view of an alternative solution,where a Schottky contact 36 is used as overvoltage diode. For this, theSchottky diode 18 can be integrated in a contact hole for contacting thegate electrode. The outer contact VS is thereby connected to the voltagesensor and is connected to a metallic lead 35 by an ohmic conductor.This metallic lead 35 forms a Schottky contact into an n-conducting orp-conducting poly region which is in connection with the first switchingelectrode 5 or with the source S.

Such a diode 17 can alternatively also be provided in a control, driveror measuring IC 44, as illustrated in FIG. 10.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

1. A rectifier circuit having a synchronously controlled semiconductorelement, comprising: at least one field effect transistor with a controlelectrode and two switching electrodes, in which the control electrodeoperates the reverse state and the forward state between the switchingelectrodes; and at least one driver which cooperates with a voltagesensor of the field effect transistor and operates this to the forwardstate during a conducting diode operating state of the field effecttransistor, wherein an output capacitance of the voltage sensor forms atleast one part of a non-linear capacitive voltage divider; wherein theoutput capacitance of the monolithically integrated voltage sensorcomprises a sensor cell region which is arranged in an insulated mannerfrom a cell field of the field effect transistor; wherein the sensorcell region is a separate cell field of the field effect transistor, andin which the cell field and the sensor cell region comprise separatesource metallizations; and wherein the source metallization of thesensor cell region is electrically connected to a trench gate structure.2. The rectifier circuit of claim 1, wherein the output capacitance ofthe voltage sensor forms a high voltage tap of the voltage divider, andan external voltage-independent capacitance forms a low voltage tap ofthe voltage divider.
 3. The rectifier circuit of claim 1, wherein thesensor cell region is surrounded by a field plate trench.
 4. Therectifier circuit of claim 1, wherein the capacitance of themonolithically integrated voltage sensor partially comprises a gateoxide of the sensor cell region as dielectric.